Propeller blades are typically formed from a structural spar which is attached at one end to a retention element. The retention element retains the blade in a hub of the propeller and is generally made from metal such as steel. It may comprise various features such as bearing races which will allow the pitch of the blade to be varied during operation. Examples of such propeller blades are disclosed in U.S. Pat. No. 5,222,297 A and US 2015/0110633 A1.
The spar is typically a fibre reinforced structure comprising a lightweight core, for example a cellular structure such as foam, which is surrounded by multiple layers of fibre reinforcement.
The spar is typically formed by attaching, for example bonding, the core to the retention element and then wrapping layers of fibre reinforcement around the core. Leading and trailing edge structures, for example foam structures, may be bonded or otherwise attached to the spar to create the blade profile, a woven fabric then wrapped around the structure, and the whole structure then impregnating with resin and cured to form the final blade assembly.
Whilst such constructions and manufacturing techniques are satisfactory, the metallic retention element may be relatively heavy and expensive to produce. Also, should any problem arise in the manufacturing process, then the whole assembly including the retention element will potentially need to be scrapped, which is costly.